A sieve-tray air stripper arrangement is a water-treatment apparatus that is used to effect the transfer of volatile organic chemicals from water (aqueous phase) to air (gaseous phase). Conventional such arrangements generally comprise a series of chambers, stacked vertically, in which each chamber is separated by a perforated plate or sieve tray. Water that is contaminated with volatile organic compounds is introduced into the top chamber, and flows across the top tray to a downcomer aperture, through which it descends to the next lower tray. The water height on each tray is controlled by the water flow rate and the height of a weir which surrounds the downcomer aperture. Water flows from the lowest tray into a sump chamber, which forms the base of the apparatus. Pumping or gravity discharge is used to maintain a constant level of treated water in the sumps.
Air is introduced into the sump chamber by means of a fan or blower, and flows upwardly through perforation holes in each of the trays. The air eventually exits through a vent stack in the top of the apparatus. Thus, the air generally flows in an opposite direction to the water. The water flowing over each sieve tray is therefore subjected to intense aeration by the air. The aeration causes a chaotic froth on each tray, and provides substantial air/water interface surface area for transfer (partitioning) of volatile organic chemicals from the aqueous phase to the air (gas phase). Thus, the air that exits from the top of the air stripper contains volatile organic constituents that were previously present in the aqueous phase.
For such a conventional arrangement, each sieve tray represents a stage of treatment, and in conventional practice each stage is built as a modular chamber to permit vertical assemblage. The top tray or chamber, which is the first stage in the treatment process, receives the water that requires treatment and allows discharge of the chemically laden stripping gas to the atmosphere. A given number of chambers, equivalent to the number of stages required for complete treatment, are stacked and clamped together to provide the completed assembly. Generally such conventional assemblies include a bottom chamber that acts as an air distribution plenum and also as a sump for the treated water.
In general, various trays or stages occasionally need service such as cleaning and/or replacement. One drawback to conventional configurations is the need to unclamp and dismantle the entire system in order to service any given tray. For example, cleaning of a tray may be needed in order to remove scaling due to water hardness or high levels of dissolved iron, which can plug the perforations. In typical, conventional systems, heavy equipment is generally needed in order to unstack the tray, since the trays and/or the stack of trays are generally heavier than can be easily handled manually.
Another problem with such conventional arrangements is generally that there has typically been no convenient way to visually judge the air distribution characteristics of each stage during operation. That is, real time interaction, while the assembly is operated, is generally limited to interpretation of instrument readings. One cannot, with conventional air strippers, observe the operation of any given stage or tray.